Spotify 'AAC_24' format (Raw AAC)

[larley]

Hi all,
I've downloaded and decrypted a track with the format 'AAC_24' from Spotify.
I already opened a thread on the 'Audio' Sub-Forum but we didn't get far and I wanted to post this in here too as this Sub-Forum is more active and it's somewhat related to Video Streaming Downloading.

A link to the unmodified (just decrypted) version of the file: https://forum.videohelp.com/attachments/80672-1720858349/file.aac
Its file header is 'SPaC' (Spotify Audio Codec?).

I hope someone has an idea.

[ProWo]

Hi all,
I've downloaded and decrypted a track with the format 'AAC_24' from Spotify.
I already opened a thread on the 'Audio' Sub-Forum but we didn't get far and I wanted to post this in here too as this Sub-Forum is more active and it's somewhat related to Video Streaming Downloading.

A link to the unmodified (just decrypted) version of the file: https://forum.videohelp.com/attachments/80672-1720858349/file.aac
Its file header is 'SPaC' (Spotify Audio Codec?).

I hope someone has an idea.

These are the FFmpeg errors in your file.
Nothing seems to fit at all.
It is probably not decrypted correctly.

[larley]

There is no "wrong decryption". Either it works or it doesn't and the file changes into a different kind of garbage data. The only way this file could be decrypted incorrectly would be if the garbage data blob arranged its bytes in a way where it looked like a file by chance but the chances of this happening is zero.

[LZAA]

Give me the original (encrypted) file.

[larley]

I'll send it when i get home, but I'm guessing you want the Key and IV too?
It's AES-128-CTR btw

[lomero]

from what i know spotify uses an encrypted audio stream. once downloaded this stream must be decrypted and then trough ffmpeg converted to m4a or aac
and there are only two audio streams available: 128 for free users and 256 for premium users

[larley]

There's also OGG_VORBIS_320/160/96 which are used by the spotify client (160 by default). I'm not sure where AAC_24 is used though. The formats you're referring to are MP4_256/128(_DUAL).

[larley]

AES-128-CTR
Key: a4c251a7b3bbab69b9f71b595cd56f8e
IV: 72e067fbddcbcf77ebe8bc643f630d93

[larley]

All of the reverse engineering I've done so far can be found here: https://github.com/DevLARLEY/spotify-oggmp4-dl

[october262]

All of the reverse engineering I've done so far can be found here: https://github.com/DevLARLEY/spotify-oggmp4-dl

try using the musicfab spotify downloader - https://www.dvdfab.cn/spotify-converter.htm?trackid=headmenu2
the have a free trial.

[larley]

All of the reverse engineering I've done so far can be found here: https://github.com/DevLARLEY/spotify-oggmp4-dl

try using the musicfab spotify downloader - https://www.dvdfab.cn/spotify-converter.htm?trackid=headmenu2
the have a free trial.

Do I look like I'm struggling to download anything from Spotify? This thread is about making an AAC file playable, and not using Chinese-owned Trial Software.

[LZAA]

631 KB is an incomprehensible size. Download encrypted audio content in full.

[larley]

This is what is returned by the Spotify API:

{
    "cdnurl": [
        "https://audio4-ak-spotify-com.akamaized.net/audio/df6087632f48c2da7a049edf3bad9f5bf672781d?__token__=exp=1721240290~hmac=41d58b07ffe385e70919abe0ba28a69b5a6349766c1eefb546e9fc96081f6f87",
        "https://audio4-fa.scdn.co/audio/df6087632f48c2da7a049edf3bad9f5bf672781d?1721240290_9URiNZuQyx8F85BuWJc4LRoVkQ9wusKZDU9cYDsSKlc="
    ],
    "fileid": "df6087632f48c2da7a049edf3bad9f5bf672781d",
    "result": "CDN",
    "ttl": 86400
}

These are whole files without any kind of range headers. Also, when compressing the track downloaded as "MP4_256" to a 24k AAC file i get an output files that's 665KB in size. I'm pretty sure that this is the complete version of the file.

[LZAA]

How long is the audio content?

[larley]

This is what ffmpeg outputs after printing 50 errors and warnings:

Input #0, aac, from '.\file.aac':
  Duration: 00:00:38.85, bitrate: 133 kb/s
  Stream #0:0: Audio: aac (LC), 3.0, fltp, 131 kb/s

[LZAA]

I'm not asking about the file. I'm asking about the content on a web resource.

[larley]

Ah, 3m 33s

[LZAA]

If the content duration is '3m 33s', then why does FFmpeg show '00:00:38.85'? Something is wrong here.
For example.
I have two audio files in an 'AAC' container:
1. 1m 2s=996 KB.
2. 3m 49s=1,97 MB.
Can you save a session in 'Fiddler'?